As a resistor provided in a micro electric circuit such as a semiconductor device, a longitudinal nano-fuse and a nano-resistor circuit element are disclosed in Japanese Laid-Open Patent Application No. JP-P2003-162954A. FIG. 1 is a view showing a structure disclosed in JP-P2003-162954A. In this structure, a longitudinal conductive spacer 30, which is formed between a top conductor 60 and a bottom conductor 10, acts as a resistor or a fuse. It is described that materials such as metals, alloys, and semiconductors can be used as the resistor (spacer 30).
In case where the resistor such as metals, alloys, and semiconductors are used as the fuse, reliability may be poor. Specifically, when the fuse is burned out by passing an electric current, a burned out part may be linked again by melted materials. Additionally, an electromigration or a stressmigration may result in a disconnection of a fuse that is not scheduled to be burned out. Providing a resistor having a high reliability is requested.
Also, in order to obtain a structure in which the resistor is embedded in a via hole as shown in FIG. 1, processes such as a damascene process, a wet etching process, and a reactive etching, are required. A manufacturing method is complex. Therefore, decreasing a number of manufacturing processes is requested.
Moreover, a high temperature (over 100 degree) process such as CVD is required when a thin film made of metals, alloys, and the like is formed on a substrate as the resistor. By the high temperature process, characteristics of a transistor and the like included in a circuit may be changed. Also, when the substrate is made of a material having low resistance against heat such as a plastic, the substrate may be damaged by heat. Therefore, the resistor made of metals, alloys, semiconductors and the like can not be easily formed on an upper layer of an integrated circuit or a plastic substrate.
In order to attain the requests described above, carbon nanotubes are watched with keen interest as the resistor. In order to obtain a resistor made of the carbon nanotubes, coating a carbon nanotube dispersion solution on a substrate and drying are only needed. The high temperature process is not required, and the number of manufacturing processes can be decreased.
When the carbon nanotubes are used as the resistor, the carbon nanotubes are required to be uniformly dispersed. However, the carbon nanotubes have high cohesive force and easily cohere in a coating solvent. Thus, the carbon nanotubes are not easy to be dispersed uniformly in the resistor.
As a related art, Japanese Laid-Open Patent Application No. JP-P2005-7561A discloses a carbon nanotube dispersion solution in which carbon nanotubes and a non-ionic surfactant are mixed in an amide type polarity organic solvent.
Also, Japanese Laid-Open Patent Application No. JP-P2002-346996A discloses, removing a dispersion solvent from a highly concentrated dispersion solution in which carbon nanotubes are dispersed in the dispersion solvent that has low viscosity, and thereby forming an electric and/or magnetic network in the carbon nanotubes. It is described that a concentration of the carbon nanotubes in the highly concentrated dispersion solution is within a range between 1 and 10 g/liter.
Also, Japanese Laid-Open Patent Application No. JP-P2005-72209A discloses, mixing carbon nanotubes in a cross-linkable coating solution, curing the solution after coating, thereby obtaining a carbon nanotube structure that has a mesh structure in which a plurality of carbon nanotube is mutually cross linked.
However, even if the techniques described above are used, uniformness of dispersion in the carbon nanotubes is limited. A technique for dispersing the carbon nanotubes more uniformly is desired. Also, even it the techniques described above are used, reliability of a resistor acting as a fuse can not be necessarily enhanced.